Photochromic eyeglasses serve as sunglasses whose lenses are quickly colored outdoors where they are irradiated by light including ultraviolet radiation like sunlight and as ordinary transparent eyeglass whose lenses are faded indoors where there is no irradiation, and demand for the photochromic eyeglass is growing nowadays.
As for photochromic eyeglass lenses, plastic lenses are particularly preferred from the viewpoints of lightweight and safety, and photochromic properties are generally provided to the above plastic lenses by compounding an organic photochromic compound. As means of compounding the compound, there are known a method in which the surface of a lens having no photochromic properties is imbibed with a photochromic compound (to be referred to as “imbibing method” hereinafter) and a method in which a photochromic compound is dissolved in a polymerizable monomer and the polymerizable monomer is polymerized to obtain a photochromic lens directly (to be referred to as “in-mass method” hereinafter).
In addition to these methods, there is also known a method (to be referred to as “coating method” hereinafter) in which a coating layer having photochromic properties (to be also referred to as “photochromic coating layer” hereinafter) is formed on the surface of a plastic lens by using a coating material containing a photochromic compound (to be also referred to as “photochromic coating material” hereinafter). However, it is not easy to achieve photochromic properties required for photochromic eyeglass lenses only with a thin photochromic coating layer, and most of photochromic lenses which have been put to practical use are manufactured by the imbibing method or the in-mass method.
However, due to the recent development of a photochromic coating material which can meet the above requirement, expectations for the coating method are sharply growing from the excellent feature of the coating method, that is, ability to provide photochromic properties easily to any lens substrate basically. For example, a soft lens substrate into which a photochromic compound is easily diffused must be used in the imbibing method and a special monomer must be used to develop excellent photochromic properties in the in-mass method. In contrast to this, there are no restrictions on the lens substrate in the coating method.
Up till now, a method in which a solution prepared by dissolving a photochromic compound in an urethane oligomer is applied to the surface of a lens substrate and cured has been known as the coating method (refer to WO98/37115). There also has been known a method in which a solution prepared by combining polymerizable monomers having one, two or three or more (meth)acrylic groups in a specific ratio and dissolving a photochromic compound in them is applied to the surface of a lens substrate and cured (refer to U.S. Pat. No. 5,914,174). There further has been known a method in which a solution prepared by dissolving a photochromic compound in a monomer composition comprising two or more polymerizable monomers having two (meth)acrylic groups is applied to the surface of a lens substrate and cured (refer to WO01/02449). There still further has been known a method in which a polymerizable monomer containing a photochromic compound, an amine compound and a radically polymerizable monomer producing a silanol group or a silanol group through hydrolysis and/or a radically polymerizable monomer having an isocyanate group is applied to the surface of a lens substrate and cured (refer to WO03/11967).
However, according to the method described in WO98/37115, since the crosslinking density of the obtained photochromic coating layer is low, the temperature dependence of photochromic properties is large and the photochromic compound may be dissolved into the hard coat solution when a hard coat layer is to be formed on the photochromic coating layer. Thus, there is room for improvement. According to the methods described in U.S. Pat. No. 5,914,174 and WO01/02449, as the photochromic properties are unsatisfactory and further adhesion between the photochromic coating layer and the hard coat layer is unsatisfactory, a special pretreatment such as plasma treatment must be carried out to form the hard coat layer. Therefore, there is room for improvement.
Meanwhile, the method described in WO03/11967 is an excellent method because the photochromic coating layer has sufficiently high adhesion and sufficiently high scratch resistance without carrying out a special pretreatment such as plasma treatment even when a hard coat layer is to be formed on the photochromic coating layer and exhibits excellent photochromic properties.
However, according to the method disclosed in WO03/11967, there is possibility that the storage stability of the photochromic curable composition may degrade. It is considered that this depends on the type and content of the polymerizable monomer in use. Further, depending on the storage state, there may arise problems that it is difficult to coat an optical substrate due to an increase in viscosity, photochromic properties deteriorate, and adhesion to the hard coat layer becomes unsatisfactory. Therefore, there is room for improvement.
According to the method disclosed in WO03/11967, an optical article having a photochromic coating layer exhibits excellent photochromic properties such as high color optical density and high fading speed at the beginning. It is considered that this depends on the type and content of the polymerizable monomer in the photochromic curable composition. However, there may occur a phenomenon that as the optical article is used for a longer time, the fading speed becomes slower (to be referred to as “delay in fading” hereinafter). Therefore, there is room for improvement.